Intermittent ulnar nerve compression due to accessory abductor digiti minimi muscle: Crucial diagnostic role of nerve ultrasound

Nerve entrapment is a common pathologic condition with a diagnosis that relies on clinical and neurophysiologic evaluations. Nerve entrapment can be caused by anatomic variations, such as accessory muscles. In the past, the diagnosis could only be made during surgical exploration, but recently ultrasonography (US) has allowed us to find atypical structures surrounding and compressing nerves. Among muscle variations, the accessory abductor digiti minimi (AADM) is the most common aberrant muscle in the Guyon canal, with an incidence of 22.4%.